Animals detect multiple kinds of stimuli, including chemicals, force, light and temperature. Distinct sensory modalities often rely on related molecular receptors2. In some cases the same receptor participates in multiple sensory modalities. How does such polymodality emerge? How can it be regulated to enable sensory discrimination? We will probe these issues by studying two classes of polymodal receptors we have identified in the fruit fly Drosophila melanogaster whose polymodality is regulated by complementary molecular mechanisms. We propose to investigate these issues in three aims. 1) We will probe the molecular mechanisms by which the activity of a receptor for both moderate warming and aversive chemicals can be regulated in a cell-specific fashion to achieve appropriate sensitivity and specificity, and use these studies to investigate the molecular basis of thermal and chemical detection in both fruit flies and Anopheles mosquitoes. 2) We will investigate how a pair of receptors act together to mediate both thermosensation and hygrosensation, and how these distinct activities are regulated to confer appropriate behavioral responses to each stimulus in both fruit flies and Anopheles mosquitoes. 3) We will test the hypothesis that multiple related receptors can function together in a combinatorial fashion to create distinct classes of sensory receptors that mediate responses to distinct sensory modalities in different sensory neurons in both fruit flies and Anopheles mosquitoes. Together, these studies will provide fundamental insights into the molecular basis of sensory receptor polymodality, how sensory receptors detect thermal and chemical stimuli, and how sensory receptor activity can be regulated to achieve appropriate sensory sensitivity and specificity.